We seek to understand molecular regulatory mechanisms controlling breast tissue development and mammary epithelial cell transformation. SWI/SNF chromatin remodeling enzymes control the accessibility of genomic chromatin and are vitally important in the initiation of multiple differentiation programmes through regulation of cell cycle progression and gene expression. These enzymes interact with tumor suppressors, and individual subunits are tumor suppressors themselves. Our studies indicate that SWI/SNF enzymes can modulate gene expression, nuclear and cellular morphology, proliferation, and tissue development in mammary epithelial cells. We also showed that knockdown of one ofthe SWI/SNF ATPase subunits results in altered nuclear shape, identifying SWI/SNF enzymes as one of the few known nudear regulatory proteins that has a role in nuclear structure. The Runx2 transcriptional regulator is expressed at elevated levels in some breast and other cancer cells. We and other P01 investigators demonstrated that RUNX2 functions as an oncogene by promoting early stages of mammary epithelial cell transformation in a manner entirely dependent on proper subnuclear localization. We propose to mechanistically address how SWI/SNF enzymes and RUNX2 promote changes in nuclear and cellular architecture that lead to cancer. Since development and malignant transformation take place in a three dimensional context, we are utilizing model systems of normal and transformed breast cells that recapitulate the microenvironment of a tissue and that permit the dynamic and reciprocal crosstalk between the extracellular matrix and nuclear gene expression. In this application, wewill investigate the physiological functions for SWI/SNF enzymes in immortalized, transformed, and metastatic mammary epithelial cells in monolayer and in three dimensional, reconstituted basement membrane culture (Aim 1). We will further probe the role ofthese enzymes in maintaining nuclear shape by exploring how loss of the factors affects various parameters of nuclear structure (Aim 2). In Aim 3, we will continue studies of RUNX2 function in mammary epithelial cell oncogenesis and will explore how SWI/SNF and RUNX2 factors may cooperate to promote cell transformation. RELEVANCE (See instructions): A hallmark of many cancers is the altered morphological and functional state ofthe cell nucleus. We have shown that key regulatory factors known to affect parameters of nuclear structure modulate cellular properties associated with mammary epithelial cell transfomation. We seek to understand the molecular basis for these observations.